The current Ford XR8 5.4-litre DOHC V8
(aka Boss 260) is a beaut engine. While the rival Holden V8 plods along with
pushrods and a single cam, the Ford donk meets world standards with its DOHC 4-valve heads, cross-ram intake manifold, high-flow Cobra intake system and
electronic throttle control. Producing 260kW and 500Nm. it epitomises everything
that a modern V8 should be.

But what do you do if you want some more
grunt? How do you improve on an engine that’s already pretty high
spec?

In this article we’ll check out what can
be achieved by whacking in some aftermarket cams - after you’ve done the usual
bolt-on breathing mods.

Preliminary Bolt-on Mods

The demo car for
this article is a BA XR8 5-speed owned by Steve Lansdowne.

Steve’s first
modifications involved upgrading the air intake and exhaust system.

The XR8 is already endowed with a high
flowing airbox and intake plumbing so there has been no need to modify any of
this. But the snorkel into the airbox is another matter. Steve has replaced the
standard snorkel with a SS Inductions ‘Big Mouth’ item which has a custom
enlarged entry. As seen in this photo, the modified entry to the snorkel is
gigantic in terms of cross sectional area – very unlikely to cause any
restriction (until the bonnet is shut, anyway!). A King Dragon high-flow filter is also fitted inside the airbox.

The only other
modification to the intake system is the fitment of an SS Inductions throttle
body. The new throttle measures 80mm diameter while the standard part is 75mm.
This represents a 14 percent increase in cross-sectional area.

The factory exhaust system has also been
replaced from headers to tip. Up front, the factory manifolds have been swapped for Di Filippo ‘Series One’ headers and a pair of high-flow cat converters has
been bolted in. From the back of the cats is an off-the-shelf Redback twin 2½
inch mandrel exhaust.

Camshaft Upgrade

The next step for Steve was the
installation of Crow camshafts and an accompanying ECU retune by
ChipTorque.

Why take this route, you ask? Well, Steve
says he enjoys the progressive output and heightened rev range that come with
the bigger cams. He’s also a bit ‘old school’...

Steve’s car served as a test bed for
prototype camshafts from Crow. The supplied camshafts are best described as
“mild street” – they offer greater top-end power while maintaining a good torque
spread and acceptable idle quality. Interestingly, the high lift camshafts
fitted to the FPV Boss 290 engine will not fit into the XR8 engine as they
require longer valve stems and other associated
modifications.

The following table compares the duration
and lift specifications of the standard BA XR8 cams with the Crow items. As you
can see, duration is increased considerably while lift is increased by a
relatively modest margin. In comparison, the FPV Boss 290 cams deliver greater
lift but less duration.

Dur @ 0.050"

Advert Dur

Lobe Lift

Std XR8

In 177

230

0.218"

Ex 177

230

0.218"

Crow XR8

In 200

255

0.234"

Ex 200

255

0.234"

Installation of the
camshafts is a big job.

ChipTorque was handed the task of fitting
all four new camshafts and, because of the XR8’s limited under-bonnet space,
it’s a process that involves removing the engine. Lachlan Riddel of ChipTorque
says it’s easiest to drop the engine onto a cradle and install the new cams at
ground level.

The new cams are installed using the
standard valve springs and cam timing is set to factory specs. It’s a job that
takes around 20 hours.

Tuning

With the long duration camshafts
installed, Lachlan Riddel retunes the factory engine management using their
X-Flash system.

X-Flash is a Windows-based software
program that gives a wide range of ECU adjustment including fuel and ignition,
rev limit, closed-loop parameters, diff ratio settings and auto transmission
shift behaviour. The ECU is flashed via the OBDII port so there’s no need to cut
any wires. However, like the EcuTeK programming software for Subarus, X-Flash
does not allow real-time tuning - it’s a case of repetitively flashing new data
into the ECU and making another dyno run.

Steve’s XR8 has been tuned to run 98 RON
high-octane fuel so you’ll find a few degrees of extra ignition advance pretty
well across the rev range. The high-load air-fuel ratio has also been set to
around 12.6:1, which is pretty safe for this type of engine. Lachlan says
there’s probably another 8 – 10 percent of injector duty cycle left to play
with.

To capitalise on the top-end kick of the
new cams, Lachlan has increased the rev limit from about 6000 to 6800 rpm. Idle
speed is also raised to around 800 rpm to enhance idle quality and drivability.

Lachlan expects that, even with its
aftermarket camshafts, the car should meet the emission standard which is
applicable to the car’s date of manufacture (ADR 97/00). A wilder set of cams
would make it extremely difficult to control hydrocarbons at idle. This is
partially because the Boss 260 engine uses MAP-based load sensing from factory -
a mass airflow meter would make the tuning task easier.

Results

This Dyno Dynamics chassis dyno graph
compares power and torque achieved before and after fitment of the new camshafts
and ECU tune (the ‘before’ curves are shown in blue and the ‘after’ curves are
shown in red). Note that the ‘before’ curves were performed with the preliminary
bolt-on mods in place.

As you can see, the standard camshafts
maintain steady torque until about 5000 rpm. Top-end torque then tails off and
peak power output is 198kW at the wheels. With the new cams and ECU tune, the
torque curve is a similar shape but is much stronger across the rev range.
Top-end torque also holds strong past 6000 rpm and, as a result, peak power
output is now 263kW at the wheels – a gain of 33
percent!

Interestingly, peak power is now achieved
at 6400 rpm (up from 5250 rpm) and peak torque arrives at around 5000 rpm (up
from 4250 rpm). On face value, this would suggest the engine is now quite peaky
– but that’s not the case. Sure, the biggest improvements are found at high rpm
but output is increased across the entire rev range.

Steve is very happy with the result. Grunt is delivered progressively and the car's much quicker than before – quick enough to run consistent
low 13 second ETs with a very gentle launch. Idle quality is well within his
boundaries of acceptance and fuel economy remains reasonable depending on
driving style. Steve says it’s possible to achieve 9 – 10 litres per 100km
consumption on the highway.

We had the opportunity to drive the
cam’d XR8 and can vouch that it’s considerably quicker than the standard Boss
260 and quicker than a FPV GT. Throttle response is strong, it’s very driveable
and much more willing to rev. Our only criticism is a surge that occurs at small
throttle openings - but we’re assured this has since been eliminated with
further tuning. The cam’d idle is much lumpier than standard but still
acceptable.

So what’s the
cost?

Well, ChipTorque charge AUD$4450 for
supply and fitment of the camshafts and ECU tune. This is in addition to the
cost of preliminary bolt-on breathing mods. In Steve’s case, he’s spent around
AUD$7000 in total and has achieved a net power gain of 42 percent (starting with
a base output of around 185kW at the wheels).

There’s no denying you can achieve greater
overall performance with a bolt-on centrifugal blower kit but this upgrade
should certainly appeal to those who aren’t fans of forced induction. At least
there are now a couple of options for tuning this already great engine...

Update – Steve has now changed the
diff ratio of his XR8 to maximise the performance from its new camshafts. The
standard 3.23:1 diff ratio has been swapped for a 3.73:1 unit and we’re told
this has improved drivability and better utilises the high rpm power output. In
short, it’s made a big difference.

The FPV Boss 290 Engine – Where does its Extra Power come
from?

Well, the 290 engine has more aggressive camshafts
(giving a definite shake at idle), different valves, followers and springs, a
balanced steel crank with reengineered rods and domed pistons. These pistons
provide a 10.5:1 compression ratio that requires 96+ RON fuel, while the 260
engine has a 9.5:1 compression ratio that’s happy to run on normal unleaded.

Output is of the FPV beast is 290kW at 5500 rpm and
520Nm at 4500 rpm.

Note that this represents a 12 percent power gain and 4
percent power gain over the Boss 260. The cam’d engine seen here produces w-a-y
more than that!